1. Field of the Invention
This invention relates to a method and apparatus for editing and combining selected portions of previously recorded audio signals to form a composite recorded audio signal.
2. Description of the Prior Art
Digital recording of audio signals on magnetic tape has been shown to offer significant performance improvements over traditional analog recording methods. However, to be fully exploited, all functions of the recording studio should be performed in the digital domain.
One function performed in the recording studio is editing. Editing refers to a process where selected audio signals recorded on separate channels of at least one tape medium are concatenated to form an edited, composite audio signal. In prior art analog systems this is typically accomplished by physically cutting the record medium and splicing appropriate sections of the medium together.
This cut and splice technique is virtually impossible to perform successfully on digitally recorded tapes because a splice introduces physical tape distortions which prevent accurate audio signal reconstruction.
Accordingly in the digital domain, audio signals are edited by a copying process. Selected portions of the audio signals present on different channels of a record medium are copied onto a separate channel of a medium to produce an edited audio signal. The selected portions of the audio signal are defined by edit points which are designated audio signal data words which define a physical location on the record medium. Typically, an entry and exit edit point will be designated to define each selected audio portion. When the entry point for the selected portion is reached, audio signal data will be transferred by a copying process from the channel on which the audio signal is present to another separate master channel. When the exit point for that selection is reached, the copying process for the selected audio section will be completed and a new audio signal from another channel will be transcribed onto the master channel.
The primary problem in defining editing points for digitally recorded audio signals involves the location of a position within the selected audio signals where a splice may be implemented without causing audible distortion of the audio waveforms at that point. Once aurally adequate edit points have been determined, it is further required that the transcribing process be performed precisely at the designated edit points. This synchronization is required because the various audio signals may have been recorded at different times on different record media.
One prior art approach to editing digitally recorded audio signals involves copying the audio signals onto a magnetic disk memory where they are manipulated and edited to form a composite or master signal on the disk medium. The principal limitation of this prior art approach is the inability to store more than a few minutes of audio signals on a disk memory.